Question
One textbook costs $10 at a shop. During a sale, for every 3 textbooks bought, the 4th textbook can be bought at a discount of 20% off the original price. How many textbooks does Liam buy if he pays $390 altogether?
4 m

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One textbook costs $10 at a shop. During a sale, for every 3 textbooks bought, the 4th textbook can be bought at a discount of 20% off the original price. How many textbooks does Liam buy if he pays $390 altogether?